How to start/stop wind blowing at a specific frame?
Make sure the force field is not hidden. Select the force field (wind) in the outliner or 3D view. The key frames you set will then show up in the timeline and in the Animation Editor. 

Insert a keyframe with a value of zero at frame 210 to stop the wind. If you want the wind to stop abruptly set a keyframe at 209 equal to the value of the keyframe before it.